Triple stimuli-responsive keratin nanoparticles as carriers for drug and potential nitric oxide release.

Development of pH/GSH/enzyme triple stimuli-responsive drug delivery system is promising for tumor therapy due to more acidic, higher glutathione (GSH) level, and overexpressed trypsin under tumor microenvironment. Herein, keratin/doxorubicin (DOX) complex nanoparticles (KDNPs) were for the first time prepared using a drug-induced ionic gelation technique without cross-linker, organic solvent and surfactant. The resultant KDNPs had high drug loading efficacy and performed considerably stable in aqueous solution. Drug delivery curves showed that KDNPs exhibited triple-responsive characters (pH, GSH, and enzyme). Under tumor microenvironments (acid and high GSH level), KDNPs performed surface charge conversion of negative-to-positive and enhanced permeation retention effect (EPR), which both benefited the drug accumulation. Furthermore, the overexpressed trypsin would cleave the peptide bonds within KDNPs and enhance the DOX release. KDNPs were demonstrated to be internalized by A549 cells through endocytosis by cellular uptake assay. Cytotoxicity assay indicated that KDNPs could inhibit the proliferation of tumor cells efficiently. In vivo cytotoxicity and hemolysis tests suggested that KDNPs exhibited excellent biocompatibility as well as good blood compatibility. In vivo antitumor efficacy demonstrated that KDNPs had a strong antitumor effect similar to that of free DOX, but with nearly no side effects. Intriguingly, KDNPs were able to catalyze endogenous NO donor in blood to release NO in tumor tissue, resulting in the prolonged blood circulation time and improved therapeutic activity of drug. In conclusion, keratin-based drug carriers are potential for cancer therapy in clinical medicine.